SB 7.12.5
sayam pratas cared bhaiksyam
gurave tan nivedayet
bhuñjita yady anujñato
no ced upavaset kvacit
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The brahmacari should go out morning and evening to collect alms, and he should offer all that he collects to the spiritual master. He should eat only if ordered to take food by the spiritual master; otherwise, if the spiritual master does not give this order, he may sometimes have to fast.